1. Field of the Invention
The present invention relates generally to interferrometric fiber optic gyroscopes (IFOGs), and more particularly to control mechanisms for improving the stability of IFOGs.
2. Background of the Invention
The scale factor stability of an IFOG is highly dependent on the stability of the wavelength observed at the system photodetector. To improve IFOG performance, especially with respect to scale factor stability, IFOGs have been provided with a wavelength control scheme based on a wavelength division multiplexer (WDM) coupler, that acts as a wavelength discriminator, and a pair of matched photodiodes. More specifically, FIG. 1 shows a highly conventional IFOG architecture that includes a light source 110, such as a fiber light source, a 50—50 power splitter 115, and integrated optics chip 118 that feeds light to and from a sensing coil 120, the latter two components sometimes being referred to herein as a “sensing loop assembly.” Fifty-fifty coupler 115 is also connected to a photodiode and associated pre-amp 125 that is used to detected the Sagnac effect caused by rotation of sensing coil 120. IFOG loop closure electronics 130 bridge photodiode 125 and IOC 118 thereby providing desirable feedback, as is well-known.
To improve upon the known system of FIG. 1, as mentioned, an architecture like that shown in FIG. 2 has recently been proposed. Here, a wavelength division multiplexer (WDM) coupler 210 along with a pair of matched diodes 220 is inserted in the optical circuit. This combination is sometimes referred to herein as a “wave division multiplexer/detector assembly.” A signal representing the sum of the matched diodes is provided to IFOG loop closure electronics 130 and a differential signal is fed to wavelength control feedback electronics 230 to provide feedback directly to light source 110, and thereby provide improved wavelength stability for the light source itself.
Unfortunately, the wavelength stability of this system depends substantially on the stability of WDM coupler 210 and matched photodiodes 220, which may be subjected to external perturbations (e.g. temperature, radiation, etc.). These components may also be susceptible to long-term drift, thereby further degrading stability.
There is therefore a need for systems and methods that still further improve the wavelength stability of IFOG devices.